Electric system for recording and reproducing sound



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E. H. HANSEN July 4, 1933.

ELECTRIC SYSTEM FOR RECORDING AND REPRODUCING SOUND Filed Oct. 25 1927 2 Sheets-Sheet 1 INV R.

2 Sheet L 2 HA N Filed Oct- 25 ELECTRIC SYSTEM FOR RECORDING AND REPRODUC-ING SOUND Emily 47 R Patented July 4, 1933 UNITED STATES ND HQHANSEN, OF NEW YORK,'1\1'. Y.

ELECTRIC 'SYSTEMEOR nnconnrue AND-REPRODUGING soUim A pp licatibn fi1ed0ct0ber 25 1927. Serial No. 22 ,597.

This invention relates to a new and improved method of recording sound waves by means of an electro-optical-chemical system, and to the distortionless reproduction of the record somade. i

A further object of my invention is to provide a novelmethod of synchronization of recorder to reproducer, which eliminates distortion due to changes of speed.

Another object of my invention is the correction of a recording light valve so that a photographic record of sound may be recorded in the true tones as originally pro duced. f

A further object of my inventionis to provide electrical circuits whereby these improvements may be accomplished in a simple and practical manner. I I Further objects of my invention will appear more fully hereinafter.

The invention conslsts substantially in the construction, combination, location, and relative arrangements of the'various parts, as shown in the accompanying drawings, and

. described in the specifications, and claims hereinafter.

With reference to the drawings:

Figure 1 is a diagrammatic view of the mechanism, and electrical circuits utilized in the recording process.

Figure 2 shows the relative form of a' slit, the image of which is thrown by optical means on to an optical wedge. 1 Figure 3 illustrates the wedge shaped 'opening through which the image shown in Figure 2 passes for correction purposes.

Figure 4 is a diagrammatic view of the .mechanism and electrical circuits utilized in the translation of reproduction of the sound record.

- liigure 5 illustrates a section of the film record obtained in accordance with my invention. 1

Thesame part is designated by the'same reference character wherever it appears;

Referring to Figure 1, a source of sound is represented bythe tuning fork 1. Sound waves from this source reach and afl'ect the microphone 2, which is illustrated. as being fof the electrostatic type and capable of rethe whole suspended in a strong magnetic sponse to all audio frequencies, any type of microphone known to the .art may be employed however. A source of potential is indicated by 3, the positiveterminal of which is connectedthrough theiresistance 4 and thence to one plate of. themicrophone. The negative terminal of-battery 3 is :connected to the opposite plate of themicrophone and it is obvious that anyv displacement of the movable plate changes thecapacity, andlikewise the current flowing in the circuit'connected with the plates.

The grid 7 ofa triode is connected by means of a. condenser 5 to a point between the resistance 4 and'the plate of microphone 2,While the filament 9 0i this triode'is. connected .to the-negative terminal of the microphone exciting battery 3, thus permitting changes in potentialacr'oss the resistor 4 to pass on and be amplified in the triode. A resistor6 is provided in regulation of the charge on grid 7. Triode filament 9 is heated by the battery I 10 and regulated by the rh-eostat 11; Plate 8 is energized through. the resistor 12 by the common battery source 3. Capacitive coupling is provided by the condenser 13 to the grid 15 of a second triode. 1

This second'triode has a filament 14 excited by a battery source 19 and controlled by a o rheostat 18.. Plate 16 of this triode is energized through a resistance 20 by energy from the common battery source 3. A A light valve consisting of a single loop of wire, a mirror 21 mounted on this loop and s5 field represented by the pole pieces 22, is energizedby current flowing through the plate resistor 20. The mirror 21 is deflected proportionally to the current flowing through the plate 16'and the resistor 20 and interprets the displacement of the plates of the microphone 2. v r

A source of light such as a concentrated filament incandescent lamp is represented by 23 and is energized by the battery 24 and the temperature is controlled bythe resistance 25. A condensing lens 26 is used to focus an image of this filament across the slit 27. The filament I have found best suited is a straight single filament the image of which is slightly larger than the aperture of slit 27 as repredeflection at certain values is non-linear due 1 was sented by Figure 2. An image of slit 27 is focussed by means of lens 28 011 to the mirror of the light valve 21, and thence to an optical compensator 29 shown in an enlarged form in Figure 3.

I have found that an optical compensator madefrom an opaque material and a wedge form cut therefrom to be most satisfactory. This optical compensator may be said to function as follows: mirror 21 is deflected both as to frequency. and amplitude, it has been found in practice however that the amplitude to the torque imposed on the loop due to twist.- This is extremely noticeable for certain pea-k volumes at high frequencies. In Figure 3 position 30a shows the position of slit image 27 when a minimum sound is affecting the microphone. Position 306 shows the change to about one half the total volume of sound, and 300 shows full amplitude of sound.

It will be observed that the "amount of light passing through the optical compensator at these three points isnot quite linear due to the cutting off of this beam of light by the wedge shape of the compensator. At the high amplitude end of. the optical compensa tor a greater amount of light than is proportionate is permitted to pass through. This light after passing through the optical co npensator falls on the condensing lens 31 which is of sufficient sizeto cover the optical comipensator and focus the beam of light so that it covers the slit 32 an image of which is in turnfocussed to apoint35 on the recording The recording light sensitive film is kept in the light tight box 34 and is placed on the reel36. This film 37 is threaded around the guide rollers '38 and 39, sprocket 40, and thence to a takeup drum 4 F A motor 41 is placed within this box and on a common shaft are connected thereto a generator 48, mercurybalance wheel 49, and

gear driven pulley 42. A flexible belt connects this drive pulley with the sprocket pulley 45b, and mounted on the sprocket is a second. pulley 4561. which 'is connected .by means of a flexible belt with a pulley 450 attached to and driving the takeup reel 44. It will be observed that'film 37 is drawn from the unexposed reel 36 and guided by rollers delity and naturalness of the recorded sound and means are hereinafter'described for correcting such variations in speed.

' The output of the generator 48 is dependent upon the speed at which the motor 41 drives it, and being mounted on a common wise be detected in the generator output. I

have therefore connected this output to a glow tube through a suitable resistance 50 Which'is set at a point allowing a predetermined value of current to flow through the glow tube.

A lens 52 focusses light from the glow tube on to a slit 53, an image of which is focussed by a lens 54 to a point 55 on the recording film 37. 'A path structure similar to that shown inFigure 5 is. obtained wherein 119 represents the exposure to the right of the figure, as made by the glow discharge, and varies only in densities as the speed of the motor and the applied voltageto the glow tube. 120 represents the striatic structure formed by deflection of the light valve due to sound displacements of the microphones and varies both as to frequency of structure and density. 1 i

' A motor controlling resistance 46 permits the recording equipment to operate at any predetermined speed, and: this in turn will expose the film to a standard density, when developedina standard developing bath for a definite period of time. Having described the method whereby a compensated sound record is placed upon the same base as a varying density record of the speed of the film,

the method of translation will be described.

Referring to Figure 4 amotor 71' has mounted upon its shaft a mercury balance wheel 75 and a gear driven pulley 70, which is connected by means of afiexible belt to pulley 69?) attached to the driving sprocket 68; The photographic record previously obtained and represented by Figure 5 is placed on-the reel 66 and threaded over the guide roller 67 and through the slit guides 101 and :5

63, and thence over the driving sprocket 68 to the takeup reel 7 6. The take upfreel isdriven by thefiexible belt connecting pulley 69a on the driving sprocket, andpulley 690 on the take up reel. The driving motor is wound type, consisting of a series circuit 74 and a shunt circuit 7 3, and inaddition an extra field winding 72. Speed regulation is primarily obtained by means of the resistance 7 7 in the power supply circuit.

A concentrated filament lamp 94 is ener- CIDO . 110 of the compound g ized by a battery 95 and is regulated'by a resistance 96. An image of this filament is focussed by means of the lens 97 until it covers a slit 98, which is similar to that represented by 27 in Figure 2. An image of this slit is focussed by means of lenses 99 and 100 through an outer plate 101 thence through the film 65, path 119. Figure 5, and through aninner slit plate 101 on to a photocell 102.

The photo-electric cell 102 may be in any of the conventional forms preferably of the potassium hydride or barium types and is energized by means of abattery source 103 through a resistor 104:. Current flows in this circuit proportionate to the amount of light falling on the photo cell after passing through the path 119 in Figure 5. I have found in practice that if the film used for reproduction has been printed and developed so as to give a transmission of forty percent, optimum operation is secured. This photo-electric cell current is then amplified by means of a direct current amplifier of conventional form. Changes in potential across the resistor104; passing through a biasing battery 105 and thence to grid 106; a connection to lower end of resistor 10 1 being made to filament 108 which is excited by battery 111 and controlled by a resistor 112. Plate 107 is energized from a battery source 109'with a filamentre turn through a resistor 110. A tap is taken off the anode of a battery 109 to the grid 113 of a second triode, which has a filament excited by battery 117 controlled through a resistor 118. The plate is energized-from a battery source 116 through a resistor 115. A' tap is taken from resistor 115 to the field '72 and thence to the lower terminal of the resistor 115. This arrangement is for the purpose of securing a suitable impedance match between the motor field 7 2 and plate circuit of the controlling triode.

It will be observed that with any particular density of path 119 a definite current will flow through the control field 72 of the driving motor 71, and that any change will cause a correction proportionate to the density of the control path 119.

In the translation of the sound path as represented by 120 in Fig. 5, a source of light 56 energized by a battery source 57 and controlled through a resistor 58 is focussed to a slit 60 the image of which is focussed by means of lenses 61 and 62 through the aperture in the slit plate 63 thence through the ably one utilizing potassium hydride or barium as an emissive agency, is energized by means of a battery source 79 through a resistor 80.

As before stated changes in the path 120, Figure 5, vary both as to the width or frequency of line and density, and photo-cell currents corresponding to these changes will be found to possess their former musical or audio frequency characteristics, and this pulsating currentiwh-en coupled to the grid 83 of triode through a coupling condenser 81 and filament 85 which is excited by a batcur to those skilled in the'art without departing from the sco-peand spirit of my invention as defined, therefore what I claim as new and useful, and of my own invention, and desire to'secure by Letters Patent is,-

1. The method of photographically recording sound on moving film which comprises simultaneously affecting the film with sound modulated light, and a second light source the intensity and frequency of which varies with the speed of an alternator driven by the same source that drives the film.

2. The method of photographically recording sound on moving film which comprises: simultaneously affecting the film with a sound modulated light and a second light source, the frequency of which varies with the speed of the moving film.

In testimony whereof, I have signed my name to this specification this 22nd day of October, 1927. V

E. H. HANSEN. 

